This invention relates to a wafer processing system and, in particular, relates to an improvement in transfer technique for transferring a wafer into an ion implantation chamber serving as an end station in an ion implantation system that is employed in, for example, the semiconductor manufacturing technology.
An ion implantation system comprises an ion source for generating ions. The ions generated in the ion source are extracted through an extraction electrode as an ion beam. Only a necessary ion species is selected from the extracted ion beam by the use of a mass analysis magnet device, a mass analysis slit, and soon. The ion beam composed of the selected ion species is implanted into a wafer in an ion implantation chamber through a deflector for scanning, acceleration/deceleration electrodes, and so on. A wafer processing system comprises the ion implantation chamber (vacuum process chamber). The wafer is transferred into the ion implantation chamber through a load lock chamber.
One example of the wafer processing system of this type will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic structural diagram of a wafer transfer device 200 in a conventional wafer processing system. The wafer transfer device 200 is provided for an ion implantation system (not illustrated). In FIG. 1, only part of a section of a housing is illustrated using a break line with respect to a vacuum chamber 203 where ion implantation is applied to a wafer. The wafer transfer device 200 comprises a loading portion 206. The loading portion 206 serves to transfer an unprocessed wafer 205 into the vacuum chamber 203 through a load lock chamber 204 while transfer a processed wafer from the vacuum chamber 203.
The loading portion 206 has a platform 208 installed in the atmosphere. An aligner 212 is installed substantially at the center of the platform 208. The platform 208 further includes thereon first and second two robots 214 and 215 for wafer transfer with the aligner 212 interposed therebetween. The platform 208 further includes thereon two cassette stations 216 installed corresponding to the first robot 214 and two cassette stations 217 installed corresponding to the second robot 215.
The aligner 212 is a device for positioning a wafer in an angular direction suitable for ion implantation. In short, the wafer is formed with a positioning cut surface and notch. The aligner 212 comprises, in addition to a rotatable positioner, a sensor light-emitting plate and a sensor light-receiving plate for detecting the positioning cut surface and notch of the wafer. The aligner 212 detects the positioning cut surface and notch of the wafer by the use of the sensor light-emitting plate and the sensor light-receiving plate and carries out positioning of the wafer by the use of the positioner.
Since the first and second robots 214 and 215 have the same structure and function, description will be given of only the first robot 214. The first robot 214 is a three-axis arm robot and is installed at a predetermined position on the platform 208. The first robot 214 has an arm structure for implementing wafer transfer in and out with respect to the load lock chamber 204 and the cassette stations 216 and is capable of upward/downward movement, rotation, and forward/backward movement.
The cassette stations 216 and 217 have a detachable cassette 218 storing a number of wafers in a stacked fashion and have a structure that is rotatable to a position facing the corresponding robot 214, 215. When the corresponding robot 214, 215 takes out an unprocessed wafer from the cassette station 216, 217, the corresponding cassette station is turned by a predetermined angle so that an opening portion thereof faces the corresponding robot. Likewise, when the corresponding robot 214, 215 stores a processed wafer 205 into the cassette station 216, 217, the corresponding cassette station is turned by the predetermined angle so that the opening portion thereof faces the corresponding robot.
In this example, the two cassette stations 216 and the two cassette stations 217 are installed with respect to the corresponding first and second robots 214 and 215, respectively, on the side opposite to the load lock chamber 204 so that the four cassette stations are provided in total. It is possible to provide a required number of cassette stations for each robot and, therefore, as long as there is room remaining in the loading portion 206, the number of cassette stations may be more than four.
FIG. 2 shows an operation principle of the robots in a wafer transfer process. The wafer transfer by the operation of the robots starts with a preparation step (first step S1) where one unprocessed wafer 205′ is taken out from a cassette A and placed on the aligner 212 by the first robot 214 in advance. The operation of this preparation step is carried out as a pre-stage when processing a first wafer. Subsequently, the following continuous operation is implemented.
In the continuous operation, the first robot 214 receives a processed wafer 205 from the load lock chamber 204 and stores it into the cassette A (second step S2). Then, the first robot 214 takes out an unprocessed wafer from the cassette A and places it on the aligner 212 (first step S1). On the other hand, the second robot 215 is in a standby state holding an unprocessed wafer that has already been subjected to a predetermined angular position adjustment on the aligner 212. Immediately after the processed wafer 205 has been taken out by the first robot 214, the second robot 215 transfers the unprocessed wafer 205′ into the load lock chamber 204 before the first robot 214 places the next unprocessed wafer on the aligner 212 (third step S3).
When the first, second, and third steps have been sequentially implemented by the two robots so that all the wafers of the cassette A have been subjected to ion implantation and stored in the cassette A, then, wafers of a cassette B are processed. In this case, the operations of the first robot 214 and the second robot 215 are reversed.
Referring to FIG. 3, the load lock chamber 204 is divided into an upper load lock chamber 231 and a lower load lock chamber 232. The upper load lock chamber 231 is configured so as to allow arms of the first and second robots 214 and 215 to be inserted thereinto and have insert portions for those arms where lock doors 234 and 235 are provided, respectively. In the load lock chamber 204, there is provided a support table 241 having a wafer receiving platen 240 for placing thereon a wafer 205 or 205′. The support table 241 has a seal 243 provided along a peripheral edge thereof. A support shaft 242 is joined to a bottom portion of the support table 241. The seal 243 serves for sealing between the upper load lock chamber 231 and the lower load lock chamber 232 cooperatively with a partition wall 245 in the load lock chamber 204. The support shaft 242 passes through a bottom wall of the lower load lock chamber 232 and is coupled to a drive mechanism (not illustrated) arranged on a lower side of the load lock chamber 204 so as to be vertically movable.
Referring back to FIG. 2, the vacuum chamber 203 is provided therein with an I-shaped transfer arm 220 that is vertically movable and rotatable. The transfer arm 220 has both ends provided with generally C-shaped retaining portions 251 each for retaining a wafer. When an unprocessed wafer 205′ placed on the wafer receiving platen 240 moves downward into the lower load lock chamber 232, the transfer arm 220 retains it by the use of one of the retaining portions 251 and turns at 180 degrees to thereby move the unprocessed wafer 205′ to the ion beam implantation side. Simultaneously with this, the other retaining portion 251 retains a processed wafer 205 on the ion beam implantation side and turns at 180 degrees to thereby place it on the wafer receiving platen 240. Then, the wafer receiving platen 240 with the processed wafer 205 mounted thereon moves upward into the upper load lock chamber 231. Subsequently, the lock door 234 (or 235) is opened so that the wafer is taken out by the arm of the first (or second) robot 214 (or 215). Naturally, when the lock door 234, 235 is opened and closed, the support table 241 surely performs sealing between the upper load lock chamber 231 and the lower load lock chamber 232.
The wafer transfer device as described above is disclosed in, for example, Japanese Unexamined Patent Application Publication (JP-A) 2000-12647.
However, there arises the following problem in the wafer processing system having the foregoing wafer transfer device that employs the single load lock chamber 204 having the two lock doors 234 and 235 and the single I-shaped transfer arm 220. An air vacuum exhaustion/ventilation time, particularly the vacuum exhaustion time, for the load lock chamber 204 is long as compared with a wafer processing time, i.e. an ion implantation time for a wafer. As a result, a standby time in the load lock chamber 204 is prolonged. Further, in the single load lock chamber 204 having the two lock doors 234 and 235, an open time of the two lock doors in total is long and therefore a loss time increases. Consequently, a throughput or processing capability as the wafer processing system is limited and, therefore, further improvement in processing capability is required.